<html>
<body>
<script type="text/javascript" charset="utf-8">
  function installBeforeUnload(removeAfterNTimes) {
    let count = 0
    window.addEventListener('beforeunload', function handler(e) {
      setTimeout(() => console.log('beforeunload'))
      if (++count <= removeAfterNTimes) {
        e.preventDefault();
        e.returnValue = '';
      }
    })
    console.log('installed')
  }
</script>
</body>
</html>
